Direct Anatomic Registration in Computer-Assisted Total Hip Arthroplasty Improves Accuracy of Acetabular Cup Alignment

BACKGROUND: Computer-assisted total hip arthroplasty using direct anatomic registration (DAR) with acetabular center axis software is an alternative method to the indirect anterior pelvic plane method. The software maps the center of hip rotation and orientation of the native acetabulum in 3 dimensions. This study aimed to evaluate the accuracy of acetabular cup alignment using DAR navigation combined with a mechanical guide device (MGD). METHODS: This prospective nonrandomized controlled study included 106 patients who underwent primary cementless total hip arthroplasty through the posterolateral approach. Fifty-four patients in the study group underwent DAR combined with MGD, whereas 52 patients underwent MGD only for acetabular cup positioning. Plain radiographs of both hips and computerized tomographic scans were obtained 2 months postoperatively for the evaluation of acetabular cup inclination and anteversion, respectively. RESULTS: The acetabular cup alignment in the study group was within the Lewinnek safe zone more than that in the control group (81.5% vs 59.6%, P < .05). The study group had a mean inclination angle of 43.88° [Formula: see text] (standard deviation [SD] 5.38) and anteversion angle of 12.82° (SD 5.99), whereas the control group had 41.10° (SD 6.79) and 12.82° (SD 9.53), respectively. There were no significant differences in estimated blood loss, length of stay, and Harris hip scores at preoperative and 3 and 6 months postoperatively, except for the operative time, which was longer in the study group (P < .01). There was 1 posterior hip dislocation in each group. CONCLUSIONS: DAR navigation combined with MGD provides better accuracy for acetabular cup positioning within the Lewinnek safe zone compared with the conventional technique.